1. Field of the Invention
The present invention relates to a sheet stacking device in which sheets are stacked, a sheet processing device which stacks processed sheets into the sheet stacking device, and an image forming apparatus which stacks sheets subjected to image formation into the sheet stacking device provided to an apparatus main body of the image forming apparatus.
2. Description of the Related Art
Conventional image forming apparatuses, such as copiers, laser beam printers, inkjet printers, facsimiles, and composite apparatuses of those devices have a sheet stacking device which is provided to an apparatus main body thereof and in which sheets subjected to image formation are stacked.
As a stacking unit for stacking sheets subjected to image formation which are delivered from a sheet delivery portion, the sheet stacking device has ascendible and descendible trays provided on multiple stages. Each of the trays on the multiple stages includes a motor, and ascends and descends (refer to Japanese Patent Application Laid-Open No. 2008-114984).
In conventional sheet stacking devices, a motor is provided to each of the trays on the multiple stages. Thus, the total thickness in an ascending and descending direction of the trays is increased, and hence the trays are ascendible and descendible actually over only short distances. This has led to a problem in that a small number of sheets are stacked on the trays.